Satellite Galaxies and Fossil Groups in the Millennium Simulation

We use a semianalytic galaxy catalogue constructed from the Millennium Simulation to study the satellites of isolated galaxies in the LCDM cosmogony. This sample (~80,000$ bright primaries, surrounded by ~178,000 satellites) allows the characterization, with minimal statistical uncertainty, of the dynamical properties of satellite/primary galaxy systems in a LCDM universe. We find that, overall, the satellite population traces the dark matter rather well: its spatial distribution and kinematics may be approximated by an NFW profile with a mildly anisotropic velocity distribution. Their spatial distribution is also mildly anisotropic, with a well-defined ``anti-Holmberg'' effect that reflects the misalignment between the major axis and angular momentum of the host halo. The isolation criteria for our primaries picks not only galaxies in sparse environments, but also a number of primaries at the centre of ''fossil'' groups. We find that the abundance and luminosity function of these unusual systems are in reasonable agreement with the few available observational constraints. We recover the expected L_{host} \sigma_{sat}^3 relation for LCDM models for truly-isolated primaries. Less strict primary selection, however, leads to substantial modification of the scaling relation. Our analysis also highlights a number of difficulties afflicting studies that rely on blind stacking of satellite systems to constrain the mean halo mass of the primary galaxies.Comment: 18 pages, 14 figures, MNRAS in press. Accepted version with minor changes. Version with high resolution figures available at: http://www.astro.uvic.ca/~lsales/SatPapers/SatPapers.htm

Micro-bias and macro-performance

We use agent-based modeling to investigate the effect of conservatism and partisanship on the efficiency with which large populations solve the density classification task--a paradigmatic problem for information aggregation and consensus building. We find that conservative agents enhance the populations' ability to efficiently solve the density classification task despite large levels of noise in the system. In contrast, we find that the presence of even a small fraction of partisans holding the minority position will result in deadlock or a consensus on an incorrect answer. Our results provide a possible explanation for the emergence of conservatism and suggest that even low levels of partisanship can lead to significant social costs.Comment: 11 pages, 5 figure

Excitons in coupled InAs/InP self-assembled quantum wires

Optical transitions in coupled InAs/InP self-assembled quantum wires are studied within the single-band effective mass approximation including effects due to strain. Both vertically and horizontally coupled quantum wires are investigated and the ground state, excited states and the photoluminescence peak energies are calculated. Where possible we compare with available photo-luminescence data from which it was possible to determine the height of the quantum wires. An anti-crossing of the energy of excited states is found for vertically coupled wires signaling a change of symmetry of the exciton wavefunction. This crossing is the signature of two different coupling regimes.Comment: 8 pages, 8 figures. To appear in Physical Review

Lattice dynamics and reduced thermal conductivity of filled skutterudites

The great reduction in thermal conductivity of skutterudites upon filling the ``void'' sites with Rare Earth (RE) ions is key to their favorable thermoelectric properties but remains to be understood. Using lattice dynamic models based on first principles calculations, we address the most popular microscopic mechanism, reduction via rattling ions. The model withstands inelastic neutron scattering and specific heat measurements, and refutes hypotheses of an anharmonic RE potential and of two distinct localized RE vibrations of disparate frequencies. It does indicate a strong hybridization between bare La vibrations and certain Sb-like phonon branches, suggesting anharmonic scattering by harmonic RE motions as an important mechanism for suppression of heat conductivity.Comment: modified version resubmitted to PRB. Results unchanged, text changed substantiall

Superconducting magnesium diboride films on Silicon with Tc0 about 24K grown via vacuum annealing from stoichiometric precursors

Superconducting magnesium diboride films with Tc0 ~ 24 K and sharp transition \~ 1 K were successfully prepared on silicon substrates by pulsed laser deposition from a stoichiometric MgB2 target. Contrary to previous reports, anneals at 630 degree and a background of 2x10^(-4) torr Ar/4%H2 were performed without the requirement of Mg vapor or an Mg cap layer. This integration of superconducting MgB2 films on silicon may thus prove enabling in superconductor-semiconductor device applications. Images of surface morphology and cross-section profiles by scanning electron microscopy (SEM) show that the films have a uniform surface morphology and thickness. Energy dispersive spectroscopy (EDS) reveals these films were contaminated with oxygen, originating either from the growth environment or from sample exposure to air. The oxygen contamination may account for the low Tc for those in-situ annealed films, while the use of Si as the substrate does not result in a decrease in Tc as compared to other substrates.Comment: 5 pages, 4 figures, 15 references; due to file size limit, images were blure

Valorización energética de la biomasa : aplicación en industrias del sector agroalimentario

La utilización de la biomasa proveniente del sector agroalimentario como una fuente de energía renovable es de gran interés en la actualidad. Ésta puede generar energía, a través de procesos tanto termoquímicos como bioquímicos, susceptible de utilizarse en forma de calor, energía mecánica o electricidad, y en diferentes estados de agregación: sólida, líquida o gas. La Digestión Anaerobia de vertidos de destilerías vínicas es un ejemplo idóneo de los procesos bioquímicos de conversión de la biomasa para obtener energía, ya que la vinaza se genera en el propio proceso de obtención del alcohol etílico (destilación de vinos y subproductos de la vinificación) producido por fermentación de una disolución azucarada y el metano se genera en la digestión anaerobia del residuo de la destilación. En este trabajo se estudia el funcionamiento y operación de diferentes tecnologías anaerobias susceptibles de ser utilizadas para la degradación de vertidos de destilerías vínicas (vinazas de vino) en condiciones anaerobias termofílicas (55°C), estableciéndose una comparación entre procesos con biomasa en suspensión y sistemas con biomasa adherida de tipo filtro anaerobio. En este último caso, además, se comparan diferentes tipos de materiales soportes y se analiza el efecto de la tasa de recirculación sobre el proceso.____________________________________Nowadays, the use of food industry biomass as a resource of renewable energy is a very interesting management alternative. Biomass can be converted to energy via thermal, biochemical and mechanical processes. This energy can be used like heat, mechanic o electric energies, and in different aggregation states (solid, liquid or gaseous). Anaerobic digestion of wine distilleries wastewater (vinasses) is a suitable example of biochemical conversion process of biomass to obtain energy. Vinasses are generated in the obtaining of ethylic alcohol on wine and wine-subproducts distillation process. This alcohol is previously generated in the biological fermentation of sugars from must. Subsequently, the biogas, mainly methane, can be obtained from anaerobic digestion of the residue of alcohol distillation, the vinasses. This work presents the main operational conditions of different anaerobic technologies used for anaerobic digestion of wine distilleries wastewater (vinasses) in the thermophilic range of temperature (55ºC). This study makes the comparison between technologies that used suspended biomass and fixed-film biorreactors (anaerobic filters). In the anaerobic filter technology there is a comparison between different support media and different recirculation rate regimes and its influence in the process